That is, in the face of the most aggressive, most highly armed, most revolutionary power the United States has ever known, deterrence worked. It worked despite serious fears about the enemy’s rationality. Indeed, it may have demonstrated that rationality is not the appropriate prerequisite for nuclear stability. Rationality can produce undesirable outcomes; it does not preclude crisis situations (Khrushchev was not insane when he ordered missiles to Cuba, he was just wrong); and in the heat of nuclear battle, rationality is unlikely to guide decisions in any country, regardless of ideology. Demanding rationality of our enemies is therefore both asking too much and asking too little. It is perhaps best that, as the scholar Kenneth Waltz has noted, “Deterrence does not depend on rationality. It depends on fear.”

Fear, after all, is an evolutionary imperative in a way that reason is not, and it induces caution in a way that can be understated by cold cost-benefit analyses. No state that values its continued existence would launch an attack that meant its own certain devastation, and there is every indication—from their oppression at home and their manipulations abroad—that the leaders of Iran and North Korea have every desire to survive. True, historically, leaders have made strategic errors that resulted in their downfall. But they did so because they miscalculated their odds of success—an error that is impossible to make in launching a nuclear strike against an adversary that clearly has the capability to retaliate. The only plausible suicide would be an assisted one in which, say, Pyongyang’s leaders feared total military defeat—deterrence does not cover “dictators in the mood of Hitler when he found himself in his final dugout,” as Churchill once put it. That means the United States shouldn’t push nuclear-armed leaders to the brink of extermination, but otherwise deterrence should hold…

…In other words, Iran is already quite bold.

Even if a nuclear-armed Iran were more aggressive, the United States could still deal with it forcefully. India and Pakistan, after all, fought directly and bloodily even when both states had nuclear weapons; and an Iranian incursion into a neighboring country could be met with force. Indeed, non-nuclear states have attacked nuclear states without apocalyptic consequences: In 1973, Israel’s nascent nuclear capability was not enough to prevent Egypt and Syria from attacking it, and, of course, in the subsequent decades it has found itself under near-constant challenge from state-sponsored terrorism and even missile attack during the Gulf war. Nor are nuclear states immune from nonmilitary regime-change efforts – there is no reason we could not support the Green Movement in a nuclear-armed Iran. We simply lose the ability to invade or militarily overthrow the regime. Which makes the rationale for attacking Iran’s nuclear program seem vaguely ridiculous: Regardless of whether we stopped or even delayed the program, we would essentially be taking military action against Iran in order to preserve our ability to take military action against Iran…

Kennedy wasn’t fully in control of the U.S. nuclear arsenal, either: According to Stanford political scientist Scott Sagan, during the [Cuban missile] crisis, Air Force officers in Montana “jerry rigged their Minuteman missiles to give themselves the independent ability to launch missiles immediately,” in gross violation of military regulations.

Whatever stability they provide then, nuclear weapons also generate a distinctly non-trivial chance of total catastrophe, and today, that chance is accentuated by the threat from nuclear terrorism. It is unlikely, but certainly not inconceivable that a state like Iran, long a sponsor of terrorism, could share nuclear technology with radicals – or that a radical sympathizer could divert fissile material from one of its enrichment facilities. States have long had trouble maintaining a perfect grip on their arsenals. When the Soviet Union broke up, it found itself riddled with poorly guarded weapons and fissile material that we are still struggling to lock up today. Pakistan’s government insists that its arsenal is secure, but the government itself is not secure. Even the U. S. arsenal has suffered numerous accidents and security problems (most notably the loss of eleven nuclear bombs during the cold war), and, in January, a group of peace activists managed to break into a NATO base where U.S. tactical nuclear weapons are stored.